It is known that stringed instruments are enhanced with age, specifically from actual playing-time (or use). The wood used to construct the instruments provides a more pleasing result the more it is vibrated. It is for this reason that such a high value is placed on vintage instruments.
The vibration associated with use of the instrument causes subtle changes in the pliability of the wood. Vibration has equal effects on the natural resins within the wood. Moreover, finishes such as lacquer, commonly applied to wooden stringed instruments, are effected by vibration resulting in the loss of plasticizers. These changes usually take many years.
Others have sought to shorten the time needed to gain the desired effects of aging. For example, U.S. Pat. No. 2,911,872 describes a motor powered apparatus which mechanically bows the strings of a violin. The system can be set up such that the strings can be played at any selected position and bowed in succession. U.S. Pat. No. 5,031,501 describes a device comprising a small shaker which is attached to the sound board of a stringed instrument. The shaker is then driven by a musical signal to simulate what the sound board experiences as it is being played. These approaches both provide automatic means to simulate playing the instrument, thus allowing the instrument to be aged without the expenditure of time or effort by a real musician. However, both approaches take a prolonged period of time to age a new instrument because they basically simulate playing the instrument; aging occurs in real time.
U.S. Pat. No. 5,537,908 developed a process for wooden stringed instruments that utilizes broadband vibration from a large electromagnetic shaker and controller. The instrument is attached to a specially designed shaker fixture and then subjected to broadband vibration excitation. The broadband input provides excitation over the frequency range of 20 to 2,000 Hz, providing accelerated aging compared to single tone inputs from earlier methods. Experienced musicians attested to hearing improvement in sound producing ability after application of this method. In addition, simple vibration measurements showed an increase in instrument response. The process, however, requires direct contact or coupling with a large electromagnetic shaker which can and result in damage to the instruments processed. In addition, the upper frequency limit of such shakers is about 2,000 Hz.